Here's the description I'll add to the mplayer man page:
---
Causes frames with higher quantizers to be more likely to trigger a
scene change detection and make libavcodec use an I-frame (default: 1).
1-16 is a sane range.
Values between 2 and 6 may yield increasing PSNR (up to approximately
0.04 dB) and better placement of I-frames in high-motion scenes.
Higher values than 6 may give very slightly better PSNR (approximately
0.01 dB more than sc_factor=6), but noticably worse visual quality.
---

Original idea from Michael; patch by me.

Originally committed as revision 4883 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4882 to svn://svn.ffmpeg.org/ffmpeg/trunk

patch by Gildas Bazin < gbazin **@** altern **.** org >

Originally committed as revision 4881 to svn://svn.ffmpeg.org/ffmpeg/trunk

patch by Gianluigi Tiesi < mplayer at@at netfarm dot.dot it >

Originally committed as revision 4880 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat.  Also fix build with --disable-muxers and --disable-ffserver.
patch by Gildas Bazin < gbazin **@** altern **.** org >

Originally committed as revision 4879 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4878 to svn://svn.ffmpeg.org/ffmpeg/trunk

Patch by Justin Ruggles jruggle earthlink net.

Originally committed as revision 4877 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4876 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4875 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4874 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4873 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4872 to svn://svn.ffmpeg.org/ffmpeg/trunk

based on a patch by Luca Abeni <  lucabe72  #@#  email  #.#  it  >

Originally committed as revision 4871 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4870 to svn://svn.ffmpeg.org/ffmpeg/trunk

Taken from a patch by Gildas Bazin < gbazin -- @@ -- altern -- . -- org >

Originally committed as revision 4869 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4868 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4867 to svn://svn.ffmpeg.org/ffmpeg/trunk

work around bug in x264 build < 44

Originally committed as revision 4866 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4865 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4864 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4863 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4862 to svn://svn.ffmpeg.org/ffmpeg/trunk

10l: now it works really, with 1k outbut buffers it failed more times, with 65k it looks safe with all samples i had

Originally committed as revision 4861 to svn://svn.ffmpeg.org/ffmpeg/trunk

Remove all possible shared libs suffixes instead.

Originally committed as revision 4860 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4859 to svn://svn.ffmpeg.org/ffmpeg/trunk

use the standard --enable-shared option.

Originally committed as revision 4858 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4857 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4856 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4855 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4854 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4853 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4852 to svn://svn.ffmpeg.org/ffmpeg/trunk

based on a patch by Luca Barbato < lu_zero -- at -- gentoo -- dot -- org >

Originally committed as revision 4851 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4850 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4849 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4848 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4847 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4846 to svn://svn.ffmpeg.org/ffmpeg/trunk

patch by Robert Swain.

probably this change is caused by the flags2 default change
why ohh why does noone run the regression tests before cvs commit :(

Originally committed as revision 4845 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 4844 to svn://svn.ffmpeg.org/ffmpeg/trunk